368 
DR. R. W. SHUEELDt’s MORPHOLOGICAL 
find a spindle-formed figure produced, which is characteristic of 
the Cypseli. 
In Swallows the bifurcation does not take place until the 
spinal tract arrives nearly at the middle of the back, and then the 
ends of the fork fail to join the rump-tract below. 
How in Humming-birds, and I have examined a great many 
excellent specimens of them, the “spinal tract” is altogether 
different from this, for it consists of a very broad, lozenge-shaped 
figure, spreading out over nearly the entire dorsal region, being 
prolonged in a wide nuchal strip which merges with the “ capital 
area” anteriorly, while its low'er angle rests upon the uropygial 
gland, and laterally spreads over the femoral region. Mesially, 
and in the middle of this lozenge-shaped area, we have a short 
longitudinal naked strip, but not nearly so conspicuous as it 
is in the Swifts. 
Indeed, the pterylography of a true Cypselus and Trochilus is 
as different in character as any two forms of birds can well be in 
this particular; and if one, unprejudiced in mind, will look at 
plate iii. of Nitzsch’s work, there will be seen a greater similarity 
between the dorsal tracts of Cypselus apus and Coracina ceplia- 
loptera than between Cypselus apus and Trochilus moschitus. 
We are already aware that, notwithstanding Swifts and 
Humming-birds possess the same number of primaries and rec- 
trices, it rather conveys the impression that this is more a matter 
of chance, when we find that they essentially differ in their ptery- 
lography and in the number of secondaries in their wings. 
For another external character in the Swifts, and a very 
excellent one, which I have failed to find elsewhere described, 
we must turn to the integuments covering the pinion. Here we 
find the entire skin exclusive of the border surrounding this part 
of the limb, and on both sides, of a deep Hack colour , being pro- 
duced by a pigmentary deposit in the skin itself. This peculiar 
character is present both in Micropus and Chcetura, while it 
is entirely absent in Trochilus. Swallows also lack this pig- 
mentary deposit in the skiu on both surfaces of the pinion. 
To conclude this chapter, then, I will make a few comparisons 
between the external forms and characters of Micropus — a true 
Swift — and Trochilus platycercus — a typical Humming-bird. 
So far as the general form of these two birds is concerned, a 
glance at PI. XXIY. figs. 37 and 39, will be sufficient to convince 
any one that they are as different as they can well be. 
